RFFE LNA topology supporting both noncontiguous intraband carrier aggregation and interband carrier aggregation

ABSTRACT

A receiver topology for supporting various combinations of interband carrier aggregation (CA) signals, intraband non-contiguous CA and non-CA signals having different combinations of signals aggregated therein.

BACKGROUND

(1) Technical Field

Various embodiments described herein relate to receivers and moreparticularly to Radio Frequency Front End (RFFE) with low noiseamplifiers for use in communications equipment configured for receivingcarrier aggregation signals.

(2) Background

Many modern electronic systems include radio frequency (RF) transceiverscapable of transmitting and receiving signals; examples include personalcomputers, wireless tablets, cellular telephones, wireless networkcomponents, televisions, cable system “set top” boxes, radar systems,etc. In communication systems that rely upon such transceivers, radiofrequencies are separated into frequency bands assigned to a particularfrequency range. For example, the IEEE (Institute of Electrical andElectronics Engineers) defines the following bands:

HF 0.003 TO 0.03 GHz HIGH FREQUENCY VHF 0.03 TO 0.3 GHz VERY HIGHFREQUENCY UHF 0.3 TO 1 GHz ULTRA HIGH FREQUENCY L 1 TO 2 GHz LONG WAVE S2 TO 4 GHz SHORT WAVE C 4 TO 8 GHz COMPROMISE BETWEEN S AND X X 8 TO 12GHz USED IN WW II FOR FIRE CONTROL, X FOR CROSS (AS IN CROSSHAIR).EXOTIC. Ku 12 TO 18 GHz KURZ-UNDER K 18 TO 27 GHz KURZ (GERMAN FOR“SHORT”) KA 27 TO 40 GHz KURZ-ABOVE V 40 TO 75 GHz W 75 TO 110 GHz WFOLLOWS V IN THE ALPHABET MM 110 TO 300 GHz MILLIMETER OR G

One example of a modern electronic system that relies upon transceiversthat transmit and receive RF signals is the cellular telephone system.For maximum compatibility in North American 2G/3G/4G, cellulartelephones are typically capable of handling dual-band 800 MHz Cellularor 1900 MHz PCS signals. In many markets, 4G data (LTE, WiMAX)transmitted and received by such cellular telephones is modulated onsignals operating at frequencies of 700 MHz, 1700-2100 MHz, 1900 MHz and2500-2700 MHz. Channels are assigned to a narrower range of frequencieswithin each band. Typically, RF signals to be transmitted are modulatedwithin one of the channels of a selected band.

Radio frequency (RF) transceivers capable of receiving such signalscomprise a receiver front end circuit that typically includes a lownoise amplifier (“LNA”). The LNA is responsible for providing the firststage amplification to a signal received within the communicationsreceiver. The operational specifications of the LNA are very importantto the overall quality of the communications receiver. Any noise ordistortion in the input to the LNA will get amplified and causedegradation of the overall receiver performance. Accordingly, thesensitivity of a receiver is, in large part, determined by the qualityof the receiver front end circuit and in particular, by the quality ofthe LNA.

In some cases, such as the case of cellular telephones noted above, theLNA is required to operate over a relatively broad frequency band and toamplify signals having several modulated baseband or intermediatefrequency (IF) signals. In some cases, the LNA of a cellular telephonemay be required to amplify a received signal having multiple modulatedIF or baseband signals. For example, some cellular telephones arerequired to receive an intraband noncontiguous carrier aggregation (CA)signal. A CA signal can have two channels (or IF carriers) havingfrequencies that are not adjacent to one another, but which lie in thesame frequency band. For example, a CA signal may have two non-adjacentchannels within a cellular frequency band defined by 3rd GenerationPartnership Project (3GPP), a well-known industry standard settingorganization.

In the case in which a receiver is required to receive a CA signal, suchas a cellular telephone that is compliant with the Release 11 of the3GPP communications industry standard, the LNA typically amplifies thereceived signal and provides the amplified output signal to a passivesplitter.

FIG. 1 is an illustration of a portion of a cellular telephone receiverfront end circuit in which an LNA 101 is coupled to a variableattenuator 103. A bypass switch 105 allows the variable attenuator to beoptionally shunted. The signal is then coupled to a single pole, threethrow mode selector switch 107 that allows the output of the LNA 101 tobe selectively coupled to only a first downconverter and basebandcircuitry (DBC) 109, a second DBC 111 or both the first and the secondDBC 109, 111.

When the mode selector switch 107 is in the first position (i.e., SingleChannel mode 1), the output of the LNA 101 is coupled directly to thefirst DBC 109. In the second position (i.e., Split mode), the output ofthe LNA 101 is coupled through a passive power splitter 113 to both thefirst and second DBC 109, 111. In the third position (i.e., SingleChannel mode 2), the output of the LNA 101 is coupled to only the secondDBC 111.

Several limitations arise from the architecture shown in FIG. 1. Thefirst limitation is the amount of isolation that can be achieved betweenthe first and second DBC 109, 111. Typically, a well-manufactured 3 dBsplitter can achieve approximately 18-20 dB of isolation between outputsat the center frequency for which the splitter 113 is designed tooperate. Signals that are cross-coupled from one DBC to the other willtypically result in interference and distortion that will result in anoverall reduction in sensitivity of the receiver.

Furthermore, passive splitters typically are designed to operateoptimally in a relatively narrow frequency range. That is, passivesplitters, by their nature are narrow band devices. As the frequency ofthe signal coupled through the splitter 113 deviates from the optimalfrequency for which the splitter was designed, the output-to-outputisolation will degrade. Due to the limitations of the splitterscurrently available, and because receivers that are designed to handleCA signals must operate in a relatively broad frequency range, thedesired isolation between the DBCs 109, 111 is difficult to achieve.

Furthermore, power splitters such as the splitter 113 shown in FIG. 1,have significant loss. Since 3 dB power splitters split the power inhalf, even an ideal splitter will result in a 3 dB reduction in power.In addition, most splitters will have an additional 1.0 to 1.5 dB ofinsertion loss. The insertion loss, like the output-to-output isolation,will typically get worse as the frequency of the signals applieddeviates from the center frequency for which the splitter was designedto operate.

Still further, the losses encountered in the mode selection switch 107and the splitter 113 lead to a need for more gain. This results inreductions in linearity (as typically characterized by measuring the“third order intercept”) and degradation of the noise figure of thereceiver when operating in Split mode.

Therefore, there is a currently a need for a CA capable receiver frontend circuit that can operate in Split mode with high output-to-outputisolation, without degraded third order intercept and noise figure, andwith relatively low front end losses.

Still further, in several cases today, it is necessary to have more thantwo inputs, each of which may receive intraband (Intra-B) CA signals oran interband (Inter-B) CA signals at different frequencies. Due tolimitations in the capability of the LNAs to handle broad frequencyranges, it may be necessary to have several LNAs, each tuned to amplifysignals in a particular frequency range. However, restrictions on thesize of a receiver front end circuit in which the LNA resides may placelimits on the number of LNAs that can be present, or at least make itnecessary to efficiently use the real estate in the integrated circuitsof the FEC.

Accordingly, there is currently a need for an efficient, flexible FECcapable of handling several possible signals, including Intra-B CAsignals in different frequency ranges and Inter-B CA signals indifferent frequency ranges, as well as non-CA signals.

SUMMARY OF THE INVENTION

A receiver front end circuit (FEC) is disclosed herein that canefficiently amplify and process single-band and multi-band RF signalswith low noise, high linearity, high isolation and small area.

A number of embodiments of the claimed invention have been described. Itis to be understood that various modifications may be made withoutdeparting from the spirit and scope of the invention. For example, someof the steps described may be order independent, and thus can beperformed in an order different from that described. Further, some ofthe steps described may be optional. Various activities described withrespect to the methods identified can be executed in repetitive, serial,or parallel fashion. It is to be understood that the followingdescriptions are intended to illustrate and not to limit the scope ofthe claimed invention, which is defined by the scope of the followingclaims, and that other embodiments are within the scope of the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a receiver front end circuit of a prior artcommunications receiver.

FIG. 2A is an illustration of an LNA circuit in accordance with someembodiments of the disclosed method and apparatus.

FIG. 2B is an illustration of the receiver portion of a front endcircuit (FEC) having an LNA such as the LNA shown in FIG. 2A, inaccordance with some embodiments of the presently disclosed method andapparatus.

FIG. 3 is an illustration of a receiver portion of an FEC in which gateswitches are coupled to gates of input FETs to allow the gates to becoupled to a known potential.

FIG. 4 is a simplified schematic of an input switch having two sections.

FIG. 5 is an illustration of a receiver portion of an FEC in accordancewith an embodiment in which the split LNA is implemented with two inputFETs and having output FETs that are shared with LNA1 and LNA 2.

FIG. 6 is an illustration of a schematic of an embodiment of thepresently disclosed method and apparatus in which a choice can be madebetween the benefits of the circuit of FIG. 2A and the benefits of thecircuit of FIG. 5.

FIG. 7 is an illustration of a schematic of a receiver FEC that is anextension of the receiver LNA circuit shown in FIG. 2B.

FIG. 8 is a simplified schematic of an LNA circuit in accordance withanother embodiment in which a fourth signal output is provided and afourth single LNA is provided.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2A is an illustration of the receiver portion of a front endcircuit (FEC) 200 (hereafter referred to as a “receiver FEC”) inaccordance with some embodiments of the presently disclosed method andapparatus. The receiver FEC 200 comprises a low noise amplifier (LNA)circuit 201. FIG. 2B is an illustration of the LNA circuit 201 with theLNA circuit 201 isolated for easier viewing. In some embodiments, theLNA circuit 201 is an LNA integrated circuit (LNAIC) that has threecircuit inputs 202, 204, 206, two circuit outputs 208, 210 and variouspower and ground connections. In some embodiments, control terminals arealso provided to allow control of the LNA circuit 201 by an outside LNAcontroller 245. Alternatively, the LNA controller 245 is fabricated onthe LNAIC 201. The LNA circuit 201 comprises two single mode LNAs, LNA1203, LNA2 209, and a split LNA 215.

The receiver FEC 200 is a flexible and efficient circuit for receivingand amplifying non-carrier aggregated (non-CA) signals, Inter-B carrieraggregated (Inter-CA) signals and intraband carrier aggregated (Intra-BCA) signals. Inter-B CA signals are signals that include two or morefrequencies of different bands. Intra-B CA signals are signals thatinclude two or more signals that are separated in frequency, but thatlie within the same band. The LNA controller 245, or other controlsystem, provides control over the three LNAs 203, 209, 215 of thereceiver FEC 200. By controlling the LNAs, a mode of operation can beselected that is appropriate to the particular signal being received.For example, for the embodiment shown in FIG. 2, the receiver FEC 200can receive one of the following four types of signals: (1) anon-carrier aggregated (non-CA) signal in a frequency range for whichLNA1 203 is tuned; (2) a non-carrier aggregated (non-CA) signal in afrequency range for which LNA2 209 is tuned; (3) an Inter-B CA signalhaving a first signal in a first frequency band to which LNA1 203 istuned aggregated with a signal in a second frequency band to which LNA2209 is tuned; and (4) an intraband CA signal having a first signal in afirst frequency band to which the split LNA 215 is tuned aggregated witha second non-contiguous signal in the same first frequency band. Whenreceiving signal type (1), LNA1 203 is turned on and the other LNAs 209,215 are turned off. When receiving signal type (2), LNA2 209 is turnedon and the other LNAs 203, 215 are turned off. When receiving signaltype (3), both LNA1 203 and LNA2 209 are turned on and the split LNA 215is turned off. When receiving signal type (4), the split LNA 215 isturned on and LNA1 203 and LNA2 209 are turned off.

In some embodiments, the two single mode LNAs 203, 209 each comprise onecascode amplifier stage (CAS) 212, 214. In some such embodiments, thetwo CASs 212, 214 are essentially the same. Therefore, for the sake ofbrevity, only the first CAS 212 is described in detail.

The CAS 212 is a two-transistor amplifier. The first transistor 205 isconfigured as a “common source” input transistor. The second transistor207 is configured as a “common gate” output transistor. In someembodiments, the transistors 205, 207 are field effect transistors(FETs). In other embodiments, the CAS 212 may have additionaltransistors (i.e., two or more stages and/or stacked transistors), notshown in FIG. 2 for the sake of simplicity. Accordingly, it should beunderstood that the simple two-transistor CAS 212 is provided as oneexample of a CAS in accordance with the presently disclosed method andapparatus. However, there are a relatively large number of alternativeamplifiers known to those skilled in the art that may be used toimplement the CAS 212.

In the CAS 212 shown in FIG. 2, the source of the output FET 207 iscoupled to the drain of the input FET 205. The signal output 220 of theCAS 212 is taken from the drain of the output FET 207. The CAS 212 canbe turned on or off by a control signal D coupled to the gate of theoutput FET 207. In some embodiments, an LNA controller 245 provides thecontrol signal D. In some such embodiments, the LNA controller 245 maybe fabricated on the same LNAIC as the LNA circuit 201 (i.e., on thesame integrated circuit (IC) as the LNAs 203, 209, 215). Alternatively,the LNA controller 245 and the LNA circuit 201 may be fabricated onseparate ICs.

Input signals to be amplified by the first LNA, “LNA1” 203, are appliedthough a circuit input 202 coupled to the gate of the input FET 205. Itshould be understood that in some embodiments the CAS 212 is the onlycircuitry in the LNA1 203. However, in other embodiments, LNA1 203 mayinclude other circuitry outside the CAS 212 not shown in FIG. 2. Suchcircuitry might include components used for impedance matching, forexample. The output of LNA1 203 is taken from the drain of the outputFET 207 and is coupled to the circuit output 208 of the LNA circuit 201.In some embodiments in which the LNA circuit 201 is fabricated as an IC,the circuit input 202 and the circuit output 208 are solder bumps thatprovide a connection point for both electrically and mechanicallyconnecting the LNA circuit 201 to other components of the receiver FEC200, such as off-chip inductors 235, 227.

In some embodiments, the input to the second LNA, “LNA2” 209, is coupledto the circuit input 206. In particular, the gate of the input FET 211of the CAS 214 of LNA2 209 is coupled to a circuit input 206. In somesuch embodiments, similar to the circuit input 202, the circuit input206 is a solder bump. A control signal G coupled to the gate of theoutput FET 213 of the CAS 214 in second LNA circuit 209 can be used toturn LNA2 209 on and off. In some embodiments, the control signal G isoutput from the LNA controller 245. In some embodiments, the onlycircuitry in LNA2 209 is the CAS 214. Alternatively, other componentsnot shown may be provided within the LNA2 209 that are outside the CAS214. The output of LNA2 209 is taken from the drain of the output FET213. In some embodiments, the output of LNA2 209 is coupled to a solderbump that serves as the circuit output 210.

The third LNA, the “split LNA” 215, comprises two CASs 216, 218. In someembodiments, each CAS 216, 218 is essentially the same as the CAS 212 ofsingle mode LNA1 203. However, the gates of the input FETs 217, 219 arecoupled together and to the circuit input 204. In this embodiment, eachof the two CASs 216, 218 of the split LNA 215 can be independentlyturned on or off. The first CAS 216 is controlled (i.e., turned on oroff) by a control signal E coupled to the gate of the output FET 221within the CAS 216. The second CAS 218 is controlled by a control signalF coupled to the gate of the output FET 223. In some embodiments, thegates of the two output FETs 221, 223 are coupled together andcontrolled by one control signal, since in most cases, the two CASs 216,218 of the split LNA 215 are turned on or off together. In someembodiments, the control signals E, F are provided by the LNA controller245. Furthermore, in some embodiments, a component 225 is coupledbetween the drain of the input FET 217 of the first CAS 216 and thedrain of the input FET 219 of the second CAS 218. In some embodiments,the component 225 is a capacitor. Alternatively, the component 225 iseither a resistor, a capacitor and resistor in series or a capacitor andresistor in parallel.

The split LNA 215 has two signal outputs. The first signal output of thesplit LNA 215 is taken from a signal output 222 of the CAS 216. Thesignal output of the CAS 216 is taken from the drain of the output FET221 of the first CAS 216. The first signal output of the split LNA 215is also coupled to the signal output 220 of LNA1 203. The second signaloutput 224 from the split LNA 215 is coupled to the signal output 224 ofthe CAS 218. The signal output 224 of the CAS 218 is taken from thedrain of the output FET 223 of the second CAS 218 and coupled to thesignal output 226 of LNA2 209. The output of LNA2 209 is coupled to theCAS signal output 226 of the CAS 214, which is taken from the drain ofthe output FET 213 and coupled to the circuit output 210 of the LNAcircuit 201.

The source of the input FET 217 of the first CAS 216 of the split LNA215 is coupled to a degeneration output 240 of the CAS 216. Thedegeneration output 240 is coupled to a degeneration output 242 of theCAS 212. The degeneration output 242 of the CAS 212 is coupled to thesource of the input FET 205 of CAS 212 and to a degeneration component231. In some embodiments, the degeneration component 231 is an inductor.

The source of the input FET 219 of the second CAS 218 of the split LNA215 is coupled to a degeneration output 244 of the CAS 218. Thedegeneration output 244 of the CAS 218 is coupled to the degenerationoutput 246 of the CAS 214. The degeneration output 246 is coupled to thesource of the input FET of CAS 214 and to a second degenerationcomponent 233. In some embodiments, the second degeneration component233 is an inductor. In some embodiments in which the degenerationcomponents are not on the LNA circuit 201, solder bumps 250, 252 areprovided to couple the degeneration outputs 240, 242, 244, 246 to thedegeneration components 231, 233.

The four control signals D, E, F, G allow the LNA controller 245 tocontrol the mode of the LNA circuit 201. In addition, in someembodiments, a general dual split input switch 241 selectively couplesone of a plurality of input filters 243 to one of the circuit inputs202, 204, 206. In some embodiments, each input signal is coupled throughan inductor 235, 237, 239. In some embodiments in which the LNA circuit201 is an LNAIC 201, the inductors are “off-chip” (i.e., not fabricatedon the LNAIC 201). In some such embodiments, the input switch 241 is onthe LNAIC 201 and the filters 243 are not on the LNAIC 201. However, inother embodiments, the inductors 235, 237, 239 may be fabricated on theLNAIC 201. Furthermore, the input switch 241 may be off-chip. Stillfurther, one or more of the filters 243 may be on-chip. In otherembodiments, any combination of on and off chip configurations ispossible.

Several operational modes can be selected for the receiver FEC 200 bydetermining the state of the input switch 241 and the control signals D,E, F, G,. For example, in the first line of a table provided in FIG. 2,a non-carrier aggregated (non-CA) signal having a frequency in thefrequency range appropriate to be amplified by LNA1 203 is received. Inthis case, the signal is routed through the input switch 241 to thecircuit input 202 (and thus to LNA1 203). In that case, the controlsignal D is set to turn on LNA1 203. The control signals E, F, G are setto turn off the CAS 214 in LNA2 209 and the two CASs 216, 218 of thesplit LNA 215. The resulting output from the receiver FEC 200 is anamplified non-CA signal at the first circuit output 208.

The second line of the table provided in FIG. 2 shows a configurationappropriate for the case in which a non-carrier aggregated signal isreceived that has a frequency in a frequency range appropriate to beamplified by LNA2 209. In this case, the signal is routed through theinput switch 241 to the circuit input 204 (and thus to LNA2 209). Thecontrol signal G is set to turn on LNA2 209. The control signals D, E, Fare set to turn off the CAS 212 in LNA1 203 and the two CASs 216, 218 ofthe split LNA 215. The resulting output from the receiver FEC 200 is anamplified non-CA signal at the second circuit output 210.

The third line of the table provided in FIG. 2 shows the case in whichan Inter-B CA signal is received by the receiver FEC 200. A first one ofthe filters 243 a is tuned to filter that portion of the signal that isappropriate to be amplified by LNA1 203. The output of that filter 243 ais routed by the input switch 241 to circuit input 202 and thus appliedto the input of LNA1 203. The portion of the signal that is appropriateto be amplified by LNA2 209 is filtered by a second one of the filters243 f. The output of the second one of the filters 243 f is routedthrough the input switch 241 to the circuit input 206 and thus to theinput of LNA2 209. The control signal G to LNA2 209 is set to turn onLNA2 209. Accordingly, an amplified signal in the frequency appropriatefor LNA1 203 is output through the first circuit output 208 and anamplified signal in the frequency appropriate for LNA2 209 is outputthrough the second circuit output 210. The two CASs 216, 218 of splitLNA 215 are turned off by the control signals E, F.

The fourth line of the table provided in FIG. 2 shows the case in whichan intraband CA signal is received by the receiver FEC 200. A third oneof the filters 243 c is tuned to filter that portion of the signal thatis appropriate to be amplified by the split LNA 215. The output of thatfilter 243 c is routed by the input switch 241 to circuit input 204 andthus applied to the input of split LNA 215. The control signals E, F tothe split LNA 215 is set to turn on both CASs 216, 218 of the split LNA215. The CAS 212 of LNA1 203 and CAS 214 of LNA2 209 are turned off bythe control signals D, G. Accordingly, an amplified signal in thefrequency appropriate for the CAS 216 of the split LNA 215 is outputthrough the first circuit output 208 and an amplified signal in thefrequency appropriate for the second CAS 218 of the split LNA 215 isoutput through the second circuit output 210. A first output loadmatching element 227 is coupled between the first circuit output 208 anda reference source (such as Vdd). In addition, a first DC blocking andoutput impedance matching capacitance 228 is coupled between the firstcircuit output 208 and a first FEC output 236. Similarly, a secondoutput load matching element 229 is coupled between the second circuitoutput 210 and a reference source (such as Vdd). In addition, a secondDC blocking and output impedance matching capacitance 230 is coupledbetween the second circuit output 210 and a second FEC output 237.

Various embodiments of the disclosed method and apparatus presentadvantages over the prior art. Examples of some of these advantagesinclude the following:

-   -   Single Mode performance is not degraded by the presence of the        split mode capability;    -   Single Mode and Split Modes are more independent of each other,        allowing for better flexibility to optimize the design in both        modes;    -   Dual Split LNA has the ability to amplify signals from two        different inputs simultaneously, i.e. similar functionality as        two single LNAs. This is done by reusing much of the hardware        already required for split mode, thus resulting in minimal        overall die size. This feature allows the Dual Split LNA to        function as a split LNA to support NC IB CA, and also as two        single LNAs to support interband CA;    -   Area savings of an LNAIC can be significant since elements of        each LNA are shared with other LNAs;    -   Isolation between LNAs and modes of LNAs is improved;

FIG. 3 is a simplified schematic of a receiver FEC 300 in which a gateswitch 302 is added to the gate of the input FET 205 to pull down thegate of the input FET 205 to a known potential, such as ground, whenLNA1 is off. Similarly, gate switches 304, 306 are provided toselectively pull down the gates of the other FETs, 211, 217, 219 to aknown potential. In some embodiments, control signals I, J, K areprovided by the LNA controller 245 and allow the LNA controller 245 toselectively open and close each of the gate switches 302, 304, 306. Byclosing the gate switches 302, 304, 306, signals that might beinductively coupled to input routes, shared source connections andshared drain connections in CASs that are off can be shunted to ground.

In addition to advantages listed above for the embodiment of FIG. 2, thegate switches of the embodiment shown in FIG. 3 increase isolationbetween different modes of operation and improve the NF performance ofthe FEC by shorting input nodes of OFF LNAs to ground.

FIG. 4 is a simplified schematic of an input switch 402, having twosections 404, 406. The input switch 402 is a simplification of the inputswitch 241 shown in FIG. 2, which has three poles and six throws. In theinput switch 241, any of the three poles can be coupled to any of thesix throws. Such a switch can be relatively complex to implement. Theinput switch 402 provides a simplification that is more limited, but iseasier to implement. The first section 404 is a two-pole, three-throwswitch that allows either of the poles 408, 410 to connect to any of thethree throws 412, 414, 416. The second section 406 is a second two-pole,three-throw switch that operates similarly. The second pole 408, 410 ofeach section 404, 406 are coupled together and coupled to the input ofthe split LNA 215. Since the second pole 408, 410 of each section 404,406 are coupled together, the input of the split LNA 215 can be coupledto any of the 6 throws 412, 414, 416, 422, 424, 426. However, the pole410 coupled to LNA1 203 and the pole 420 coupled to LNA2 209 are limitedin that each can only be coupled to one of the three throws ofassociated section. In some implementations, such a simplification ofthe input switch is appropriate, since an input signal that can only berouted to one of the LNAs can nonetheless be routed to the desiredoutput of the receiver FEC 200 by an output switch. Accordingly, as longas each input signal can be routed to at least one of the LNAs, LNA1 203or LNA2 209, an appropriate output switch (not shown) can ensure thatany input signal can be routed to any output of the receiver FEC 200.

FIG. 5 is an illustration of a receiver FEC 500 in accordance with anembodiment in which the split LNA 515 is implemented with two input FETs217, 219 and the output FETs are shared with LNA1 203 and LNA2 209. Thatis, the input FETs 217, 219 share the output FETs 207, 213 of LNA1 203and LNA2 209, respectively. The drain of the first input FET 217 of thesplit LNA 515 is coupled to the source of the output FET 207 of LNA1203. The source of the input FET 217 of the split LNA 515 is coupled tothe source of the input FET 205 of LNA1 203. Similarly, the drain of thesecond input FET 219 of the split LNA 515 is coupled to the source ofthe output FET 213 of LNA2 209. The source of the input FET 219 of thesplit LNA 515 is coupled to the source of the input FET 211 of LNA2 209.Configuring the split LNA 515 in this way changes the location of theadditional capacitive loading present in the circuit by the addition ofthe split mode support (i.e., from the nodes 208 and 210 as in FIG. 2,to the drains of FETs 205 and 211). The additional capacitive loading atnodes 208 and 210 increases the reactance of the node impedance, whichcauses lower max achievable gain and narrower matching bandwidth. Whenthe loading is instead present at the drains of FETs 205 and 211 as inFIG. 5, the previous degradations are reduced, but the noise figure canbe worsened due to the additional output noise contribution of theoutput FETs 220 or 213 caused by the parasitic current path through thecapacitive loading of input FETs 203 or 505. Accordingly, in someimplementations, the configuration of FIG. 5 may be preferable. However,in other implementations, the configuration of FIG. 2 may be preferable.It should be noted that the gate switches 302, 304, 306 of FIG. 3 (notshown in FIG. 5 for the sake of simplicity) may be used in the receiverFEC 500 of FIG. 5. In addition, the LNA controller 245 is not shown inthe receiver FEC 500 of FIG. 5 for the sake of simplicity. However, theLNA 245 may be provided in the receiver FEC 500. Furthermore, the inputswitch 402 shown in FIG. 4 may be used in place of the input switch 241show in FIG. 5.

In addition to those advantages noted above, the embodiment shown inFIG. 5 saves additional area and can result in higher max achievablegain and matching bandwidth, at the expense of higher noise figure.

FIG. 6 is an illustration of a schematic of an embodiment of thepresently disclosed method and apparatus in which a choice can be madebetween the benefits of the circuit of FIG. 2 in which the split LNA 215comprises four FETs and the benefits of the circuit of FIG. 5 in whichthe split LNA 515 comprises only two FETs. That is, the split LNA 215comprises four FETs 217, 219, 221, 223 the same as the split LNA 215 ofFIG. 2. However, a first switch 602 selectively connects the drain ofthe input transistor 217 to the drain of the input transistor 205 of thefirst CAS 212 through an input transistor drain node 624 of the firstCAS 212. A second switch 604 selectively connects the drain of the inputtransistor 219 to the drain of the input transistor 211 of the secondCAS 214 through an input transistor drain node 626 of the second CAS214. These two switches 602, 604 are provided to allow the output FETs221, 223 to be removed from the active circuit while maintaining cascodeoperation of the second CAS 214 through cascode transistor 207. A thirdswitch 606 and a fourth switch 608 are provided to couple the drains ofthe output FETs 221, 223 of the split LNA 215 to the drains of theoutput FETs 207, 209 of LNA1 203 and LNA2 209, respectively. Theseswitches (602, 604, 606, and 608) may be implemented as FET switches.Accordingly, by opening the first two switches 602, 604 and closing thesecond two switches 606, 608, the receiver FEC 600 operates the same asthe receiver FEC 200 of FIG. 2. However, when the first two switches602, 604 are closed and the second two switches 606, 608 are open, thesplit LNA 215 of FIG. 6 operates similar to the split LNA 515 of FIG. 5.It should be clear to those skilled in the art that the gate switches308, 310, 312 shown in FIG. 3 may be provided for use with the receiverFEC 600 of FIG. 6. Furthermore, the input switch 402 shown in FIG. 4 maybe used in place of the input switch 241 show in FIG. 6. In addition,the LNA controller 245 is not show in the receiver FEC 600 of FIG. 6 forthe sake of simplicity. However, the LNA 245 may be provided in thereceiver FEC 600.

The embodiment shown in FIG. 6 has the advantage of enablingcustomization of an LNAIC to allow changes in the configuration of theLNAIC after manufacturing. This allows the LNAIC performance to bealtered to match several different requirements, thereby improving theoverall system performance. This capability can be used to reduce thesize of the inventory necessary to handle various different performancerequirements.

FIG. 7 is an illustration of a schematic of a receiver FEC 700 that isan extension of the receiver FEC 200 shown in FIG. 2. That is, thereceiver FEC 700 has an LNA circuit 701 comprising six LNAs 203, 209,215, 702, 706, 712. A first of the three is a single mode LNA, “LNA1”203, that comprises one CAS 203. A second is a single mode LNA, “LNA2”209, that comprises one CAS 214. A third is a single mode LNA, “LNA3”706, that comprises CAS 707. The CAS 707 is similar to the CAS 203 andCAS 214 described above with respect to the single mode LNA1 203 andLNA2 209 of FIG. 2.

In addition, the LNA circuit 701 comprises three split LNAs 215, 702,712, similar to the split LNA 215 described above with respect to FIG. 2as well as three single mode LNAs, 203, 209, and 706, each similar tothe two LNAs 203, 209 of the embodiment of FIG. 2. Each split LNA isassociated with two single mode LNAs. For example, the split-1 LNA 215is associated with single mode LNA1 203 and LNA2 209. In this context,being associated means that the first signal output of the split-1 LNA(i.e., the signal output 222 of the first CAS 221) is coupled to thesignal output of LNA1 203 (i.e., the CAS signal output 220 of the CAS212). Furthermore, the degeneration output 240 of the first CAS 216within the split-1 LNA 215 is coupled to the degeneration output 242 ofthe CAS 212 of LNA1 203. By having the signal outputs and degenerationoutputs coupled, the CAS 212 of LNA1 203 is in parallel with the firstCAS 216 of the split-1 LNA 215. Similarly, the second CAS 218 of thesplit-1 LNA is coupled in parallel with the CAS 214 of LNA2 209.

Likewise, split-2 LNA 702 is associated with single mode LNA2 209 andsingle mode LNA3 706. Therefore, the first CAS 703 of split-2 LNA 702 iscoupled in parallel with the CAS 214 of LNA2 209 and the second CAS 705of split-2 LNA 702 is coupled in parallel with the CAS 707 of LNA3 706.

Lastly, split-3 LNA 712 is associated with single mode LNA3 706 andsingle mode LNA1 203. That is, the first CAS 709 of split-3 LNA 712 iscoupled in parallel with the CAS 707 of LNA3 706 and the second CAS 711of split-3 LNA 712 is coupled in parallel with the CAS 212 of LNA1 203.

Each of the six LNAs 203, 209, 215, 702, 706, 712 has an input 202, 204,206, 704, 708, 714. By selectively turning on or off each of the LNAs,the signal that is routed to each of the three FEC signal outputs 716,718, 720 can be selected from among: (1) a non-CA signal coupled to asingle mode LNA associated with the particular FEC signal output; (2) anintraband CA signal coupled to the one of the two split LNAs coupled tothe FEC signal output; (3) an Inter-B CA signal coupled to the singlemode LNA coupled to the FEC signal output. For example, a non-CA signalcan be coupled to the input 202 to LNA1 203 and output through the FECsignal output 716. Alternatively, a non-CA signal can be coupled toeither the input 206 to single mode LNA2 209 or to the input 708 tosingle mode LNA3 706 and output from the FEC signal output 718, 720associated with the input. In yet another scenario, an intraband CAsignal can be coupled to the input to one of the three split LNAs 215,702, 712 and two carrier aggregated signals can be output on the twosignal outputs associated with the split LNA to which the input signalis coupled. In yet another scenario, an Inter-B CA signal can be coupledto two or more of the three single mode LNAs 203, 209, 706 to allow theCA signals of each band to be output through one of the three FEC signaloutputs.

FIG. 8 is a simplified schematic of an LNA circuit 800 in accordancewith yet another embodiment in which a fourth signal output 806 isprovided and a fourth single LNA, LNA4 802 is provided. A seventhcircuit input 804 is also provided and coupled to the gate of an inputFET 805 of a CAS 803 within LNA4 802. The signal output 806 from LNA4802 is coupled to the second signal output of split-3 LNA 712. Thedegeneration output of LNA4 is coupled to the second degeneration outputof split-3 LNA 712. Accordingly, two Intra-B CA signals, each of adifferent frequency band, can be received concurrently. The first can becoupled to the input of the split-1 LNA 215 and the second to the inputof the split-3 LNA 712. The two aggregated signals of the first Intra-CAsignal would be output through the first and second circuit outputs 208,210. The two aggregated signals of the second Intra-B CA signal would beoutput through the third and fourth circuit outputs 710, 806.Alternatively, an Inter-B CA signal in which four signals have beenaggregated could be applied to the inputs of each of the four singleLNAs, LNA1 203, LNA2 209, LNA3 706 and LNA4 802. Each of the fouraggregated signals would be output from a respective one of the fourcircuit outputs 208, 210, 710, 806. Other combinations of Intra-B CAsignals and Inter-B CA signals may also be received. Furthermore, thebasic concept shown here can be extended to include as many outputs asdesired.

In addition to advantages listed above, the embodiments shown in FIGS. 7and 8 increase the number of different bands that can be supported by asingle LNAIC. With ever- increasing complexity in modern radio devices,expansion of the core concept to a large number of bands is clearly ofvalue for certain system requirements. It will be obvious to person ofordinary skill that further expansion of the concept to more bands isenvisioned by the current descriptions of the current exemplaryembodiments.

A number of embodiments have been described. It is to be understood thatvarious modifications may be made without departing from the spirit andscope of the claimed invention. For example, some of the steps describedabove may be order independent, and thus can be performed in an orderdifferent from that described. Further, some of the steps describedabove may be optional. Various activities described with respect to themethods identified above can be executed in repetitive, serial, orparallel fashion. Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, serially “stacking” components (particularly FETs) to withstandgreater voltages, and/or using multiple components in parallel to handlegreater currents. Additional circuit components may be added to enhancethe capabilities of the disclosed circuits and/or to provide additionalfunctional without significantly altering the functionality of thedisclosed circuits.

Various embodiments can be implemented to meet a wide variety ofspecifications. Unless otherwise noted above, selection of suitablecomponent values is a matter of design choice. Various embodiments ofthe disclosed method and apparatus may be implemented in any suitable ICtechnology (including but not limited to FET structures), or in hybridor discrete circuit forms. Integrated circuit embodiments may befabricated using any suitable substrates and processes, including butnot limited to standard bulk silicon, silicon-on-insulator (SOI),silicon-on-sapphire (SOS) bipolar, GaAs HBT, GaN HEMT, GaAs pHEMT, andMESFET technologies.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the following claims, and that other embodiments arewithin the scope of the claims. (Note that the parenthetical labels forclaim elements are for ease of referring to such elements, and do not inthemselves indicate a particular required ordering or enumeration ofelements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

What is claimed:
 1. A low noise amplifier (LNA) circuit having at leasta first, second and third circuit input and having at least a first andsecond circuit output, the LNA circuit comprising: (a) a first LNAcomprising a first cascode amplifier stage (CAS) having a CAS input anda CAS signal output, the CAS input coupled to the first circuit input:(b) a second LNA comprising a second CAS having a CAS input and a CASsignal output, the CAS input of the second CAS coupled to the thirdcircuit input; and (c) a third LNA comprising a third CAS and fourthCAS, each having a CAS input and a CAS signal output, the CAS signaloutput of the third CAS and the CAS signal output of the first CAScoupled to the first circuit output, the CAS signal output of the secondCAS and the CAS signal output of the fourth CAS coupled to the secondcircuit output, and the input of the third CAS and the input of thefourth CAS coupled to the second circuit input.
 2. The LNA circuit ofclaim 1, wherein each CAS comprises at least one input transistor and atleast one cascode transistor, the transistors being field effecttransistors (FETs) having a drain, source and gate.
 3. The LNA circuitof claim 1, further comprising a capacitor coupled between the sourceterminals of the cascodes of the third and fourth CAS.
 4. The LNAcircuit of claim 1, further comprising a resistor coupled between thesource terminals of the cascodes of the third and fourth CAS.
 5. The LNAcircuit of claim 1, further comprising a series capacitor and resistorcoupled between the source terminals of the cascodes of the third andfourth CAS.
 6. The LNA circuit of claim 1, further comprising a parallelcapacitor and resistor coupled between the source terminals of thecascodes of the third and fourth CAS.
 7. A receiver front end circuit(FEC) comprising the LNA circuit of claim 1, two FEC signal outputs andthree FEC inputs, each CAS further comprising a degeneration output, thereceiver FEC further comprising: (a) a first output load matchingelement coupled between a first reference potential and a first of theFEC signal outputs; (b) a second output load element coupled between thefirst reference potential and a second of the FEC signal outputs; (c) afirst degeneration element coupled between the degeneration output ofthe first CAS and the third CAS and a second reference potential; and(d) a second degeneration element coupled between the degenerationoutput of the second CAS and the fourth CAS and the second referencepotential.
 8. The receiver FEC of claim 7, further comprising: (a) afirst input matching element having a first and second terminal, thefirst terminal of the first input matching element coupled to the firstcircuit input; (b) a second input matching element having a first andsecond terminal, the first terminal of the second input matching elementcoupled to the second circuit input; and (c) a third input matchingelement having a first and second terminal, the first terminal of thethird input matching element coupled to the third circuit input.
 9. Thereceiver FEC of claim 8, further comprising an input switch having aplurality of switch inputs and a first, second and third switch output,the first switch output coupled to the second terminal of the firstinput matching element the second switch output coupled to the secondterminal of the second input matching element, the third switch outputcoupled to the second terminal of the third input matching element, theswitch being capable of selectively coupling: (a) the first inputmatching element to a switch input selected from a first groupcomprising at least two of the switch inputs; (b) the second inputmatching element to a switch input selected from a second groupcomprising at least two of the switch inputs; and (c) the third inputmatching element to a switch input selected from a third groupcomprising at least two of the switch inputs.
 10. The receiver FEC ofclaim 9, further comprising a plurality of filters, each having a filterinput and a filter output, wherein the filter output of each of theplurality of filters is coupled to a respective unique one of the switchinputs.
 11. The receiver front end circuit of claim 7, wherein each CASfurther includes a control terminal, and wherein the receiver front endfurther includes an LNA controller having a plurality of controlleroutputs, each controller output coupled to a corresponding controlterminal to selectively turn on and off the first, second, third andfourth CAS under the control of the controller.
 12. The receiver frontend circuit of claim 11, further comprising an input switch having aplurality of switch inputs and a first, second and third switch output,the first switch output coupled to the second terminal of the firstinput matching element, the switch being capable of selectivelycoupling: (a) the first input matching element to a switch inputselected from a first group comprising at least two of the switchinputs; (b) the second input matching element to a switch input selectedfrom a second group comprising at least two of the switch inputs; and(c) the third input matching element to a switch input selected from athird group comprising at least two of the switch inputs; the LNAcontroller further having at least one controller output coupled to theinput switch to provide a control signal from the LNA controller to theinput switch to control which inputs to selectively couple to each inputmatching element.
 13. The receiver FEC of claim 12, wherein the LNAcontroller outputs the control signal to the input switch incoordination with the output signals coupled from the LNA controller tothe control terminals of each of the CASs.
 14. The receiver front endcircuit of claim 13, further comprising at least one gate switch, eachgate switch coupled to the input terminal of one CAS to selectivelycouple the input terminal of the CAS to ground, each gate switch alsohaving a control input coupled to the LNA controller, the LNA controllercontrolling each such gate switch in coordination with the controlsignals I, J, K coupled to the control terminals of each the gateswitches, such that the input terminal of each CAS is coupled to groundin coordination with turning off the CAS to which gate switch iscoupled.
 15. The LNA circuit of claim 1, wherein the performance of thefirst LNA is designed to match the performance of the second LNA. 16.The LNA circuit of claim 1, wherein at least one of the performance ofthe third and fourth CAS is designed to match the performance of one ofthe first or second CAS.
 17. The LNA circuit of claim 1, wherein thesize of components of the first and second LNA are optimized for variousfrequency bands.
 18. The LNA circuit of claim 1, wherein the size ofcomponents of the third and fourth CASs are optimized for variousfrequency bands.
 19. The LNA circuit of claim 1, further comprising: (a)a third circuit output; (b) a fourth, fifth and sixth circuit input; (c)a fourth LNA having a fifth CAS, the fifth CAS having a CAS inputcoupled to the fourth circuit input, CAS signal output and degenerationoutput, the CAS signal output and degeneration output coupled to the CASsignal output and degeneration output of the fourth CAS, respectivelyand a sixth CAS having a CAS input, CAS signal output and a degenerationoutput, the CAS input of the sixth CAS coupled to the CAS input of thefifth CAS; (d) a fifth LNA having a seventh CAS having a CAS inputcoupled to the fifth circuit input, a CAS signal output and adegeneration output, the CAS signal output coupled to the third circuitoutput and to the CAS signal output of the sixth CAS and thedegeneration output of the seventh CAS coupled to the degenerationoutput of the sixth CAS; and (e) a sixth LNA having an eighth CAS andninth CAS, each having a CAS input coupled to the sixth circuit input, aCAS signal output and a degeneration output, the CAS signal output anddegeneration output of the eighth CAS coupled to the output anddegeneration output of the seventh CAS, respectively and the CAS signaloutput and degeneration output of the ninth CAS coupled to the outputand degeneration output of the first CAS, respectively.
 20. The LNAcircuit of claim 19, further comprising: (a) a fourth circuit output;(b) a seventh circuit input; and (c) a seventh LNA having a tenth CAS,the tenth CAS having a CAS input coupled to the seventh circuit input,and a CAS signal output and degeneration output coupled to the CASsignal output and degeneration output of the ninth CAS, respectively.21. A low noise amplifier (LNA) circuit having a first, second and thirdinput circuit input and having a first circuit output and a secondcircuit output, the LNA circuit comprising: (a) a first LNA comprising afirst CAS having a CAS input, a CAS signal output, an input transistordrain node and a degeneration output; (b) a second LNA comprising asecond CAS having a CAS input, a CAS signal output, an input transistordrain node and a degeneration output; and (c) a third LNA comprising afirst and second input transistor each input transistor having a first,second and third terminal: (1) the first terminal of the first inputtransistor of the third LNA coupled to the input transistor drain nodeof the first CAS; (2) the first terminal of the second input transistorof the third LNA coupled to the input transistor drain node of thesecond CAS; (3) the second terminal of the first input transistor of thethird LNA coupled to the degeneration output of the first CAS; (4) thesecond terminal of the second input transistor of the third LNA coupledto the degeneration output of the second CAS; and (5) the third terminalof the first input transistor of the third LNA coupled to the thirdterminal of the second input transistor of the third LNA.
 22. The LNAcircuit of claim 21, the third LNA further comprising: (a) a first andsecond cascode transistor, each having a first, second and thirdterminal, the source of the first cascode transistor coupled to thedrain of the first input transistor and the source of the second cascodetransistor coupled to the source of the second input transistor; (b) afirst switch coupled between the drain of first input transistor of thethird CAS and the input transistor drain node of the first CAS, thefirst switch having a first, second and control terminal, the firstterminal of the first switch coupled to the first terminal of the firstinput transistor of the third CAS, the second terminal of the firstswitch coupled to the input transistor drain node of the first CAS, suchthat the first switch selectively connects the first terminal of thefirst input transistor to the input transistor drain node of the firstCAS; (c) a second switch coupled between the second input transistor andthe input transistor drain node of the second CAS, the second switchhaving a first, second and control terminal, the first terminal of thesecond switch coupled to the first terminal of the second inputtransistor of the third LNA, the second terminal of the second switchcoupled to the input transistor drain node of the second CAS, such thatthe second switch selectively connects the second terminal of the secondinput transistor to the input transistor drain node of the second CAS;(d) a third switch having a first, second and control terminal, thefirst terminal of the third switch coupled to the drain of the firstcascode transistor of the third LNA, the second terminal of the thirdswitch coupled to the CAS signal output of the first CAS; and (e) afourth switch having a first, second and control terminal, the firstterminal of the fourth switch coupled to the drain of the second cascodetransistor of the third LNA, the second terminal of the fourth switchcoupled to the CAS signal output of the second CAS.
 23. A front endcircuit (FEC) for operation in one of four modes comprising: (a) a firstLNA tuned to a first frequency and having an output coupled to a firstFEC output; (b) a second LNA comprising two CASs, the first CAS tuned toa second frequency within a first frequency band and having an outputcoupled to the first FEC output, and the second CAS tuned to a thirdfrequency within the first frequency band and having an output coupledto a second FEC output; and (c) a third LNA tuned to a fourth frequencywithin a second frequency band and having an output coupled to thesecond FEC output; wherein in the first mode coupling a non-carrieraggregated (non-CA) signal to an input of the first LNA and attaining anoutput signal at the first FEC output, in the second mode, coupling anon-CA signal to the third LNA and attaining the output from the secondFEC output, in the third mode, coupling an interband CA signal to theinput of both the first and the third LNA and attaining the output atboth the first and second FEC output, and in the fourth mode, couplingan intraband non-contiguous CA signal to the inputs of both of the CASsof the second LNA and attaining the output at the first and second FECoutput.